Children who don't know better might throw spitballs or pull hair to get another child's attention, and it turns out that certain monkeys do something similar. Female capuchin monkeys have been observed throwing rocks at males as a form of courtship.

This study involves an animal with the incredibly appropriate scientific name Sapajus libidinosus, the bearded capuchin monkey. Researchers observing capuchin monkeys in Serra da Capivara National Park, Brazil, over a two-year study watched three female monkeys from a particular group throwing stones at males during their proceptive sexual phase. During a later period, they observed three other females from the same group were observed performing the same stone-throwing behavior during their proceptive phases. The females did not throw stones outside of their proceptive phase, suggesting that this was a specific courting behavior. Males were not observed throwing stones.

It's not clear whether this behavior is widespread among capuchins, however. There has been a similar report of a single female capuchin at a zoo throwing stones at males during her estrus, but otherwise there are no known observations of this behavior. However, the researchers here note that every time one of the Serra da Capivara monkeys successfully hit a male with her rock, the male copulated with her. While it's not clear whether being hit with a rock has any effect on the male's desire to copulate, the researchers suggest that perhaps the females in the group witnessed the success of using a rock to attract a mate and emulated that behavior. It's possible that this is a learned social behavior, rather than female capuchins having some instinct to throw rocks at the boys.